Porous Honeycomb Self-Assembled Monolayers: Tripodal Adsorption and Hidden Chirality of Carboxylate Anchored Triptycenes on Ag

Abstract

Molecules with tripodal anchoring to substrates represent a versatile platform for the fabrication of robust self-assembled monolayers (SAMs), complementing the conventional monopodal approach. In this context, we studied the adsorption of 1,8,13-tricarboxytriptycene (Trip-CA) on Ag(111), mimicked by a bilayer of silver atoms underpotentially deposited on Au. While tripodal SAMs frequently suffer from poor structural quality and inhomogeneous bonding configurations, the triptycene scaffold featuring three carboxylic acid anchoring groups yields highly crystalline SAM structures. A pronounced polymorphism is observed, with the formation of distinctly different structures depending on preparation conditions. Besides hexagonal molecular arrangements, the occurrence of a honeycomb structure is particularly intriguing as such an open structure is unusual for SAMs consisting of upright-standing molecules. Advanced spectroscopic tools reveal an equivalent bonding of all carboxylic acid anchoring groups. Notably, density functional theory calculations predict a chiral arrangement of the molecules in the honeycomb network, which, surprisingly, is not apparent in experimental scanning tunneling microscopy (STM) images. This seeming discrepancy between theory and experiment can be resolved by considering the details of the actual electronic structure of the adsorbate layer. The presented results represent an exemplary showcase for the intricacy of interpreting STM images of complex molecular films. They are also further evidence for the potential of triptycenes as basic building blocks for generating well-defined layers with unusual structural motifs.

Cyano-Substituted Triptycene-Based Monolayers on Au(111): Tripodal Adsorption, Dipole Engineering, and Charge Transfer

“…It was demonstrated that both these molecules adopt dense, nested hexagonal structures upon SAM formation, exhibiting also large-area structural uniformity, tripodal bonding configuration, and nearly upright molecular orientation, characteristic to the full extent of the Trip-(CH 2 -SH) 3 SAMs and to a lesser, but still satisfactory, extent of the Trip-(CH 2 −SH) 3 monolayer. 28 The next logical steps would be to test other anchoring groups, mediating the assembly of the triptycene-based molecules on a broad variety of substrates, 29 and to perform the decoration of the triptycene scaffold with functional tail groups. The latter issue is the subject of the present study.…”

Introduction of Triptycene with a Particular Substitution Pattern into Polymer Chains Can Dramatically Improve the Structural and Rheological Properties

“…As expected, only broad halos were observed for amorphous poly-1,4-Trip and copoly-1,4-Trip 0.32 (Figure d,e). In sharp contrast, poly-1,8-Trip, copoly-1,8-Trip 0.30 , and copoly-1,8-Trip 0.075 all displayed a set of clear diffraction peaks (Figure a–c), which are typically observed for 1,8­(,13)-substituted triptycenes assembling into a “2D + 1D” structure (Figure g). − , In the q region larger than 8 nm –1 , the XRD peaks with d -spacings of 0.70, 0.40, and 0.35 nm are due to diffractions from the (100), (110), and (200) planes of a 2D hexagonal structure (Figure g, a = 0.80 nm) formed by nested packing of the 1,8-substituted triptycene units in the polymer chains. The XRD peaks in the q region smaller than 8 nm –1 can be assigned to be one- to third-order diffractions from a 1D layered structure.…”

“…We recently reported that 1,8,13- and 1,8-substituted triptycenes self-assemble to form a specific structure with a long-range order, where two-dimensional (2D) sheets formed by nested hexagonal packing of the triptycene units stack into a one-dimensional (1D) layer. − We have also shown that telechelic polymers terminated with 1,8-substituted triptycene units, as well as three-arm star polymers with a junction point composed of a 1,8,13-substituted triptycene, self-assemble into the “2D + 1D” structure, resulting in a remarkable improvement of the rheological properties, compared to reference polymers that contain triptycene units with a different substitution pattern . Motivated by these findings, we investigated how simple linear polymers with 1,8-substituted triptycene units in the main chains (Figure b) behave in the solid state.…”

Triptycene‐Based Molecular Rods for Langmuir‐Blodgett Monolayers

“…However, the absence of crystallographic data cannot exclude polymorph B from consideration. It is worth mentioning that recent literature also describes honeycomb‐like arrangement for triptycene‐based tripodal systems, [42] but this geometry was excluded from our consideration since corresponding experimentally determined APM was much larger comparing to our values.…”